Field
Embodiments of the present disclosure generally relate to an improved large area substrate thin film transistor device, and method of fabrication thereof. More specifically, embodiments of the present disclosure generally relate to a large area substrate amorphous and LTPS thin film transistor device.
Description of the Related Art
OLED (Organic Light Emitting Diode) & Liquid Crystal Displays (LCDs) are frequently used for flat panel displays. Liquid crystal displays generally contain two glass substrates joined together with a layer of liquid crystal material sandwiched therebetween. The LCD display utilizes light emitting diodes for back lighting. OLED displays utilize an array of LTPS transistors to drive current through deposited Organic Light Emitting material. As the resolution requirements for LCDs & OLEDs increase, it has become desirable to fabricate transistors with good drive current and low off state leakage current. In a modern display panel, more than 1,000,000 pixels may be present. At least the same number of thin film transistors (TFTs) is formed on the glass substrate so that each pixel can be switched between an energized and de-energized state relative to the other pixels disposed on the substrate. Silicon containing materials have been used to form thin film amorphous silicon layers. These layers are then converted to Poly Silicon using Excimer Laser Annealing. This polycrystalline silicon (polysilicon) is referred to as low temperature polysilicon (LTPS) TFT and as an element utilized in forming a transistor used as a switch to turn pixels on and off. Unlike amorphous silicon TFTs, LTPS TFTs exhibit good switching properties. However, the problem with LTPS is something known as the floating body effect, which affects the transistor device characteristics. When a charge accumulates, the LTPS transistor exhibits similar results to that of silicon on insulator, that is the body of the device tends to float up due to hot carrier scattering, making the pixels harder and harder to switch off causing the LTPS transistors to have poor off state leakage current. To address this issue, it has been proposed to combine the use of low temperature polycrystalline silicon and metal oxide. However, the combination of LTPS and metal oxide would be extremely difficult and costly.
Therefore, there is a need in the art for an improved display device and method of fabrication thereof.